Apparatus for removing gas from molten metal during continuous casting

ABSTRACT

This is apparatus for applying vibrations to a slab of cast metal emerging from a continuous-casting mold at a position along the slab at which the interior of the slab is still molten, and for adjusting the frequency of the vibrations to be in resonance with the portion of solidified metal skin around the slab between the position at which the vibrations are applied and the point at which the skin is formed in the mold. The amplitude of the vibrations are thus adjusted to facilitate the escape of uncombined oxygen from the molten metal in the mold.

United States Patent 1111 3,55

[72] Inventor Joseph D- Gl' co [56] References Cited UNITED STATESPATENTS 3 1 9: 1968 4 2,763,040 9/1956 Korb l64/71X v lf g' {9713,447,480 6/1969 B0dille,.|l. l64/83X 1 [73] Assignee ConcostIncorporated FOREIGN PATENTS New York, N-Y. 178,432 5/1954 Austria164/283 a corporation oi Delaware 722,314 1/1955 Great Britain 164/260Division of 513344 Primary Examiner-J. Spencer Overholser 1965 3,397,733Assistant Examiner-R. Spencer Annear Attamey- Sandoe, Neill, Schottler &Wikstrom ABSTRACT: This is apparatus for applying vibrations to a [54]APPARATUS FOR REMOVING GAS FROM slab of cast metal emer fr gmg om aconunuous-castmg mold at METAL DURING CONTINUOUS a position along theslab at which the interior of the slab is still 3 claim 2 D in F molten,and for adjusting the frequency of the vibrations to be 8 in resonancewith the portion of solidified metal skin around [521 [1.8. 164/260, theslab between the position at which the vibrations are ap- 164/282 pliedand the point at which the skin is formed in the mold. [51] int. n 822d11/12 The amplitude of the vibrations are thus adjusted to facilitate[50] Field of Search 164/71, 82, the escape of uncombined oxygen fromthe molten metal in 83, 260, 261, 282 the mold.

APPARATUS FOR REMOVING GAS FROM MOLTEN METAL DURING CONTINUOUS CASTINGThis is a division of application Ser. No. 513,244 filed Dec. 13, 1965,now Pat. No. 3,397,733, dated Aug. 20, 1968.

' This invention is apparatus for continuously casting of rimming steel.

In continuous casting of steel, molten steel is poured into the upperend of an open-ended mold'which is cooled by a liquid, such as water,circulated in the mold walls. The molten metal in contact with the moldwall is cooled and solidifies to form a skin or sheath around the moltenmetal.

The cast metal leaves the bottom of the mold in a continuous ribbon orcast. The ultimate length of the continuous cast, of course,depends'uponthe amount of molten metal poured into the mold. Casts of indefinitelength can thus be continuously cast.

The length of the mold employed in continuous casting of steel isrelatively short. As the molten metal moves through themold the metal incontact with the mold wall is cooled and solidifies. At the point wherethe cast slab leaves the mold there is only a relatively thin skin orsheath of solid metal at the exterior of the slab. Theremainder of themetal in the slab is molten and is contained in the slab bythe skin ofsolid metal. As the slab moves away from the bottom of the mold themolten metal continues to cool and solidify, from the exterior of theslab inwardly, increasing the thickness of the skin or sheath until,finally, the entire cast slab is solid. The point where completesolidification of the slab occurs is at a substantial distance below thebottom of the mold, as much as'35 feet, or more, from the mold bottom insome operations. As the slab emerges from the mold, the slab issupported by rollers engaging the slab from its opposite sides. Some ofthese rollers are driven and control the speed of the slab.

The melt for continuous casting of rimming steel is prepared at atemperature of about 2,950 to 3,060 F. The melt is poured into a ladleand from the ladle into the tundish. From the tundish the molten metalis delivered to the continuous casting mold at a temperature of about2,800 to 2,875 F.

To obtain the desired rimming action, a regulated amount of uncombinedoxygen is left in the molten-metal at the time of pouring in thecontinuous casting of rimmingsteel. This uncombined oxyg'en, as themetal solidifies, forms gas in the mo]- ten metal. This gas agitates themolten metal, causing the metal to circulate in a pattern. Thiscirculation produces the desired rimming action. ltis, ofcourse,desirable that this gas, as it forms in the molten metal, move tothe top of the molten metal and escape. Any gas present in the moltenmetal at the time the metal solidifies is trapped and forms undesirablevoids or occlusions in the slab. These voids or occlusions, when theyoccur, result in flaws and defects when the continuously cast slab islater rolled. v

A substantial portion of the cooling and solidification of the metal incontinuous casting occurs belowthe mold as the cast slab moves away fromthe mold bottom. The uncombined oxygen still in solution in the moltenmetal is carried along with the molten metal in the slab until themolten metal is cooled. Thus, at a point in the cast substantiallydistant from the point where the molten metal is poured into the mold,gas bubbles are still forming.

One of the objects of the instant invention is to provide an improvedmethod for continuous casting of rimming steel.

A further object is to provide apparatus for carrying out such method.

A further object is to provide such a method and apparatus whereindissolved oxygen which, when it reacts to form a gas, will escape fromthe cast.

Still a further object is to provide continuous castings of rimmingsteel which can be rolled into relatively thin sheets without flaws ordefects on the surface of the sheets.

These and other objects will be more apparent from the followingdescription and attached drawings in which:

FIG. 1 illustrates schematically apparatus of the invention forcontinuously casting steel, viewed from one edge of the slab being cast;and I 4 FIG. 2 is a view similar to FIG. 1 but viewed from one side ofthe slab with parts of the apparatus omitted.

Many attempts have heretofore been made to apply vibratory forces tocontinuous casting operations. For the most part. these prior attemptshave involved vibration of the mold or the slab after the metal in theslab is solidified. Such prior attempts employed rugged, expensiveequipment, required specially designed molds and had many disadvantages.In addition, they were not effective in removing gas occlusions andvoids in the continuously cast slab.

In the instant invention, vibration is applied to the cast slab while asubstantial portion of the slab is molten. The shell of solid metalaround the molten metal is vibrated so that the tapered walls of solidmetal agitate the molten metal within the slab. The agitation causes thegases to separate from the solidifying surface, move upward through themolten metal in the slab center, and escape. In addition, the vibrationagitates the molten metal in the mold, causes the molten metal to 1center of the slab is still molten. These vibrators are in contact withthe opposite edges of the slab and impart vibration to the solid metalaround the exterior of the slab. From the point where this vibrationforce is applied, upward of the slab and into the mold area, thethickness of the solid metal wall around the molten metal progressivelydecreases. This progressive decrease in solid metal thickness has beendiscovered, in the instant invention, to result in a tuning action. Theupwardly extending arms of solid metal act as tuning forks, or a tunedhorn, with the center filled with liquid molten metal.

The vibration input, at the point where the vibratory force is appliedto the slab, is relatively low. However, the progressive decrease inthickness of the solid metal from the input point to the point where themolten metal is initially cooled and the skin or shell of solid metalbegins to form, results in an increase in vibration amplitude from thepoint of input to the point in the mold where the walls of solid metalinitially form.

This increase in amplitude correspondingly increases the of movement ofthe cast slab by conventional means not shown. In its downward travel,mold 6 is driven at a speed slightly faster than that of the castbeingcontinuously formed and is moved upward at a higher speed, all inaccordance with conventional continuous casting of steel procedures.

Mold 6 is open atits top and bottomQVertical beams 8, 10 are disposed inparallel position below the open bottom of mold 6. Each beam 8, 10 isprovided with a plurality of rollers 12, the rollers being relativelyclosely spaced vertically along the beams on the facing sides of beams8, l0.

Vibrator'l4 is mounted on support l6'intermediate beams 8, 10. A shoe 18having, at its opposite vertical ends, outwardly turned portions 20, 22,is connected to, and driven by, vibrator 14. Preferably, two vibratorsare employed, one at either edge of the cast slab.

In operation, molten metal is poured from a source, not shown, into theupper open end of tundish 2. The molten metal flows through nozzle 4into the open upper end of mold 6. The flow of metal through nozzle 4'isregulated, in known manner, to maintain the level of molten metal in themold cavity at the required height.

Liquid, such as water, is circulated in the walls of mold 6 to cool thewalls. As the molten metal passes through mold 6, the

metal in contact with the walls is cooled and the metal solidifies,forming a shell or sheath of solid metal around the molten metal in thecenter of the mold cavity. Thus, while in the mold cavity, solid metal bcommences to form as a shell or sheath around molten metal a.

When the cast slab emerges from the bottom of the mold 6. the shell orsheath of solid metal [2 is relatively thin. As the slab moves away fromthe bottom of mold 6, cooling continues. This cooling may besupplemented by spraying a liquid, such as water, against the slab asthe continuously forming slab travels away from the bottom of mold 6.Cooling progresses from the exterior of the slab inwardly. Additionalmolten metal a solidifies on the interior of the shell or sheath ofsolid metal b, thickening the shell or sheath of solid metal until,finally, at a substantial distance below the mold, all of the metal inthe cast is solidified.

The cast, as it emerges from the mold, comes into contact with rollers12 carried on beams 8, 10. Rollers l2 maintain the slab in alignment andsupport the slab during cooling. These rollers may be idle rollers ormay be driven. Preferably, some of the rollers are idle and others aredriven. The drive on the driven rollers regulates the speed at which thecontinuous cast is formed.

Vibrators 14, through shoes 18, vibrate the cast, from its oppositeedges, in the direction of the arrows in FIG. 2. The vibrators arelocated on the apparatus below the mold bottom where the wall of solidmetal in the cast is relatively thick but the center portion of the castslab is of molten metal. The vibratory force applied to the cast,through the solid metal b, agitates the molten metal a in the cast andcauses gas bubbles, as they form on solidification of the metal, toseparate from the solidifying surface and move upwardly through themolten metal in a direction opposite to the travel of the continuouscast.

The vibration input may be tuned to the resonant frequency of the solidmetal b in the walls of the solid metal shell above the vibrators. Theamplitude and frequency required for resonance will, of. course, varywith the size of the cast, the amount of cooling and the like, but canbe readily determined by observing the activity of the molten metal inthe mold. The amplitude and frequency of the vibrators are adjusted tobring the surface of the molten metal in the mold to the desiredagitation. The amplitude of vibration of the solid metal shell increasesfrom the point of vibration input as the thickness of the solid metaldecreases. Thus the agitation imparted to molten metal a by vibration ofsolid metal b increases from the vibration input point upwardly into themold cavity. By regulating the vibration input, agitation of the moltenmetal in the mold can be controlled. This control of the agitationpermits the molten metal to form a rim of solid metal around the L'.(-terior of the continuously cast slab and facilitates the movement ofimpurities away from the surfaces of the slab in addi tion to decreasingvoids and occlusions near the slab surfaces.

The capacity of the vibrator will, of course. depend on the size of thesteel slab to be continuously cast and. preferably, should be of a typethat can be regulated. An air-powered vibrator having a capacity oflO0,0()0 pounds thrust and a frequency up to 3,000 cycles/min. has beenfound particularly suited for the production of continuously castrimming steel slabs having a thickness of l0 inches and a width of 52inches.

The terms and expressions which have been employed are used as terms ofdescription and not of limitation, and there is no intention, in the useof such terms and expressions, of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope ofthe inventionclaimed.

lclaim:

1. ln apparatus for continuously casting metal having an open-ended moldadapted to receive molten metal in one end and to cool the peripheralportion of the metal in the mold to form therein a slab having a shellof solidified metal around a core of molten metal, means for drawingsaid slab continuously from the other end of said mold, and means forsuhsequently cooling said slab to solidify the slab all the way through,the improvement comprising vibration-producing means supported on saidapparatus for engaging and applying vibratory force to the surface ofthe shell of a slab emerging from said mold at a portion of said slab atwhich its core is still molten, said vibration-producing meanscomprising a vibrator having a shoe portion engaging the peripheralsurface ofa slab emerging from said mold at a point between the mold andsaid means for drawing the slab from the mold, said shoe portion havingits ends that are in line with the direction of movement of said slabturned outwardly therefrom, and said vilirationproducing means beingadapted for adjusting the frequency and amplitude of the vibrations itproduces to cause the portion of the shell of the slab between saidportion of the slab and the top of said shell in the mold to vibrate atresonance and to produce an adjustable degree ofagitation ofthe surfaceofthe molten metal in the mold.

2. The apparatus of claim 1 in which said vibration-producing means isan air-powered vibrator.

3. The apparatus of claim I in which said vihration-produc ing meanscomprises a pair of vibrators supported to respectively engage oppositesides of said slab.

2. The apparatus of claim 1 in which said vibration-producing means isan air-powered vibrator.
 3. The apparatus of claim 1 in which saidvibration-producing means comprises a pair of vibrators supported torespectively engage opposite sides of said slab.